diff -rupN postgresql-8.4.0-orig/src/backend/access/heap/heapam.c postgresql-8.4.0-ra/src/backend/access/heap/heapam.c
--- postgresql-8.4.0-orig/src/backend/access/heap/heapam.c	2009-06-11 16:48:53.000000000 +0200
+++ postgresql-8.4.0-ra/src/backend/access/heap/heapam.c	2009-08-08 10:41:15.000000000 +0200
@@ -135,6 +135,8 @@ initscan(HeapScanDesc scan, ScanKey key,
 	{
 		if (scan->rs_strategy == NULL)
 			scan->rs_strategy = GetAccessStrategy(BAS_BULKREAD);
+		
+		scan->rs_readahead_pages = 4096;	/* TODO: GUC ? or maybe put it in AccessStrategy ? */
 	}
 	else
 	{
@@ -766,6 +768,12 @@ heapgettup_pagemode(HeapScanDesc scan,
 			if (page == 0)
 				page = scan->rs_nblocks;
 			page--;
+			
+			/*
+			 * do some extra readahead (really needed for compressed files)
+			 */
+			if( scan->rs_readahead_pages && !finished )
+				PrefetchBuffer( scan->rs_rd, MAIN_FORKNUM, page - scan->rs_readahead_pages + ((page >= scan->rs_readahead_pages) ? 0 : scan->rs_nblocks));
 		}
 		else
 		{
@@ -788,6 +796,13 @@ heapgettup_pagemode(HeapScanDesc scan,
 			 */
 			if (scan->rs_syncscan)
 				ss_report_location(scan->rs_rd, page);
+			
+			/*
+			 * do some extra readahead (really needed for compressed files)
+			 */
+
+			if( scan->rs_readahead_pages && !finished && (page & 4096))
+				PrefetchBuffer( scan->rs_rd, MAIN_FORKNUM, (page + scan->rs_readahead_pages) % scan->rs_nblocks );
 		}
 
 		/*
@@ -1209,6 +1224,7 @@ heap_beginscan_internal(Relation relatio
 	scan->rs_strategy = NULL;	/* set in initscan */
 	scan->rs_allow_strat = allow_strat;
 	scan->rs_allow_sync = allow_sync;
+	scan->rs_readahead_pages = 0;
 
 	/*
 	 * we can use page-at-a-time mode if it's an MVCC-safe snapshot
diff -rupN postgresql-8.4.0-orig/src/include/access/relscan.h postgresql-8.4.0-ra/src/include/access/relscan.h
--- postgresql-8.4.0-orig/src/include/access/relscan.h	2009-01-01 18:23:56.000000000 +0100
+++ postgresql-8.4.0-ra/src/include/access/relscan.h	2009-08-08 09:44:38.000000000 +0200
@@ -35,6 +35,7 @@ typedef struct HeapScanDescData
 	BlockNumber rs_startblock;	/* block # to start at */
 	BufferAccessStrategy rs_strategy;	/* access strategy for reads */
 	bool		rs_syncscan;	/* report location to syncscan logic? */
+	int			rs_readahead_pages;	/* if non-zero, issue a Prefetch to get a page rs_readahead_pages ahead of current page */
 
 	/* scan current state */
 	bool		rs_inited;		/* false = scan not init'd yet */